Inspection apparatus

ABSTRACT

An inspection apparatus includes beam generation means, a primary optical system, a secondary optical system and an image processing system. Irradiation energy of the beam is set in an energy region where mirror electrons are emitted from the inspection object as the secondary charged particles due to the beam irradiation. The secondary optical system includes a camera for detecting the secondary charged particles, a numerical aperture whose position is adjustable along an optical axis direction and a lens that forms an image of the secondary charged particles that have passed through the numerical aperture on an image surface of the camera. In the image processing system, the image is formed under an aperture imaging condition where the position of the numerical aperture is located on an object surface to acquire an image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 14/677,086 filedApr. 2, 2015, which claims the benefit of Japanese Patent ApplicationNo. 2014-077591 filed Apr. 4, 2014, each of which is incorporated hereinby reference in its entirety.

FIELD

The present technology relates to an inspection apparatus that inspectsdefects of a pattern formed on a surface of an inspection object, andspecifically, to an inspection apparatus that captures secondary chargedparticles varying properties of a surface of an inspection object, formsimage data, and inspects a pattern and the like formed on the surface ofthe inspection object on the basis of the image data at a highthroughput, and an inspection method.

BACKGROUND AND SUMMARY

A conventional semiconductor inspection apparatus supports a 100 nmdesign rule and technologies. Samples as inspection objects are wafers,exposure masks, EUV masks, NIL (nanoimprint lithography) masks, andsubstrates; the samples have thus been varying. At present, apparatusesand technologies that support a design rule for samples with 5 to 30 nmare required. That is, it is required to support L/S (line/space) or hp(half pitch) nodes of 5 to 30 nm in a pattern. In the case where aninspection apparatus inspects such samples, it is required to achieve ahigh resolution.

Here, “samples” are exposure masks, EUV masks, nanoimprint mask (andtemplates), semiconductor wafers, substrates for optical elements,substrates for optical circuits and the like. The samples includesamples with patterns and samples without patterns. The samples withpatterns include samples with asperities and samples without asperities.Patterns are formed of different materials on the samples withoutasperities. The samples without patterns include samples coated with anoxide film and samples with no oxide film.

Problems of the conventional inspection apparatuses are summarized asfollows.

A first problem is insufficient resolution and throughput. In aconventional art of a mapping optical system, the pixel size is about 50nm, and the aberration is about 200 nm. Achievement of further highresolution and improvement of the throughput require reduction inaberration, reduction in energy width of irradiation current, a smallpixel size, and increase in current intensity.

A second problem is that, in the case of SEM inspection, the finer thestructure to be inspected, the more serious the throughput problem is.This problem occurs because the resolution of an image is insufficientif a smaller pixel size is not used. These points are caused because theSEM forms an image and inspects defects on the basis of edge contrast.For instance, in the case of a pixel size of 5 nm and 200 MPPS, thethroughput is approximately 6 hr/cm². This example takes a time 20 to 50times as long as the time of mapping projection. The time is unrealisticfor inspection.

Such conventional inspections are disclosed in WO2002/001596,JP2007-48686A and JP1999(H11)-132975

However, in a conventional inspection apparatus, it is difficult toinspect irregularities in a surface of an inspection object with highcontrast and also to detect very small foreign matters. Thus, it hasbeen desired to further improve the technology for inspectingirregularities in a surface of an inspection object with high contrast.

It is desirable to provide an inspection apparatus capable of inspectingirregularities in a surface of an inspection object with high contrast.

One embodiment is an inspection apparatus including beam generationmeans that generates any of charged particles and electromagnetic wavesas a beam, a primary optical system that irradiates an inspection objectheld in a working chamber with the beam, a secondary optical system thatdetects secondary charged particles occurring from the inspection objectand an image processing system that forms an image on the basis of thedetected secondary charged particles, in which irradiation energy of thebeam is set in an energy region where mirror electrons are emitted asthe secondary charged particles from the inspection object due to thebeam irradiation, the secondary optical system includes a camera fordetecting the secondary charged particles, a numerical aperture whoseposition is adjustable along an optical axis direction and a lens thatforms an image of the secondary charged particles that have passedthrough the numerical aperture on an image surface of the camera, and inthe image processing system, the image is formed under an apertureimaging condition where the position of the numerical aperture islocated on an object surface to acquire an image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational view showing main configuration components inan inspection apparatus according to an embodiment taken along line A-Aof FIG. 2.

FIG. 2A is a plan view of the main configuration components of theinspection apparatus shown in FIG. 1 taken along line B-B of FIG. 1.

FIG. 2B is a schematic sectional view showing another embodiment of asubstrate installation device of the inspection apparatus of theembodiment.

FIG. 3 is a sectional view showing a mini-environment device of FIG. 1taken along line C-C.

FIG. 4 is a diagram showing a loader housing of FIG. 1 taken along lineD-D of FIG. 2.

FIGS. 5A and 5B are enlarged views of a wafer rack. FIG. 5A is a sideview. FIG. 5B is a sectional view taken along line E-E of FIG. 5A.

FIG. 6 is a diagram showing a variation of a method of supporting a mainhousing.

FIG. 7 is a variation of the method of supporting a main housing.

FIG. 8 is a schematic diagram showing an overview of a configuration ofa light irradiation electronic optical device.

FIG. 9 is a diagram showing the entire configuration of the inspectionapparatus according to an embodiment.

FIG. 10 is a diagram schematically showing a double pipe structure of asemiconductor inspection apparatus according to an embodiment.

FIG. 11 is a diagram showing a configuration of an electron beaminspection apparatus according to an embodiment.

FIG. 12 is a diagram showing an electron beam inspection apparatus towhich the present technology is applied, according to an embodiment.

FIG. 13 is a diagram showing an example of a configuration where anelectron column of a mapping optical system inspection apparatus and anSEM inspection apparatus are provided in the same main chamber,according to an embodiment.

FIG. 14 is a diagram showing a configuration of an electron columnsystem according to an embodiment.

FIG. 15A and FIG. 15B are a view illustrating the principle.

FIG. 16A and FIG. 16B are a view illustrating an aperture imagingcondition (NA imaging condition) in one embodiment.

FIG. 17 is a view illustrating a focus adjustment under the NA imagingcondition in one embodiment.

FIG. 18 is a view illustrating the focus adjustment under the NA imagingcondition in one embodiment.

FIG. 19A and FIG. 19B are a view illustrating the focus adjustment underthe NA imaging condition in one embodiment.

FIGS. 20a to 20b is a view illustrating the focus adjustment under theNA imaging condition in one embodiment.

FIG. 21 is a view illustrating a deviation of an incident angle of aprimary beam in one embodiment.

FIG. 22 is a view illustrating a conventional adjustment method of theincident angle of the primary beam.

FIG. 23 is a view illustrating an incident angle adjustment under the NAimaging condition in one embodiment.

FIGS. 24a to 24c is a view illustrating how an NA imaging image is seenif the incident angle differs in one embodiment.

FIG. 25 is a view illustrating an adjustment method of the incidentangle of the primary beam in one embodiment.

FIGS. 26a to 26b is a view illustrating the adjustment method of theincident angle of the primary beam in one embodiment.

FIG. 27 is a view illustrating the adjustment method of the incidentangle of the primary beam in one embodiment.

FIG. 28 is a view illustrating a conventional adjustment method of asecondary system.

FIG. 29 is a view illustrating an adjustment method of the secondarysystem in one embodiment.

FIG. 30 is a view illustrating the adjustment method of the secondarysystem in one embodiment.

FIGS. 31a to 31b is a view illustrating the adjustment method of thesecondary system in one embodiment.

FIG. 32 is a view illustrating the adjustment method of the secondarysystem in one embodiment.

FIG. 33 is a view illustrating a conventional shading correction.

FIGS. 34a to 34b is a view illustrating a shading correction in oneembodiment.

FIG. 35 is a view illustrating the shading correction in one embodiment.

DETAILED DESCRIPTION OF NON-LIMITING EXAMPLE EMBODIMENTS

An inspection apparatus includes beam generation means that generatesany of charged particles and electromagnetic waves as a beam, a primaryoptical system that irradiates an inspection object held in a workingchamber with the beam, a secondary optical system that detects secondarycharged particles occurring from the inspection object and an imageprocessing system that forms an image on the basis of the detectedsecondary charged particles, in which irradiation energy of the beam isset in an energy region where mirror electrons are emitted as thesecondary charged particles from the inspection object due to the beamirradiation, the secondary optical system includes a camera fordetecting the secondary charged particles, a numerical aperture whoseposition is adjustable along an optical axis direction and a lens thatforms an image of the secondary charged particles that have passedthrough the numerical aperture on an image surface of the camera, and inthe image processing system, the image is formed under an apertureimaging condition where the position of the numerical aperture islocated on an object surface to acquire an image.

Accordingly, when the inspection object is irradiated with the beam, themirror electrons are emitted from the inspection object. Because aheight at which the mirror electrons are reflected changes depending onthe state of irregularities in the surface of the inspection object, adifference in contrast is created. Also, the mirror electrons differ inorbit from the secondarily released electrons. In such a situation, theimage is formed under an imaging condition (aperture imaging condition)where the position of the numerical aperture is located on the objectsurface to acquire an image: a crossover of the mirror electrons isaligned with the center of the numerical aperture. This can allow aninspection of irregularities in the surface of an inspection object withhigh contrast.

Also, in the inspection apparatus, the secondary optical system mayinclude focus adjustment means that adjusts a focus under the apertureimaging condition.

Accordingly, the focus is adjusted under the aperture imaging condition.For example, if the focus is moved toward a minus direction, foreignmatters in the surface of the inspection object come to be seen in theblack color. Conversely, if the focus is moved toward a plus direction,foreign matters in the surface of the inspection object come to be seenin the white color. Thus, the inspection of irregularities in a surfaceof an inspection object can be provided with high contrast.

Also, in the inspection apparatus, the primary optical system mayinclude incident angle control means that controls an incident angle ofthe beam with which the inspection object is irradiated.

This controls the incident angle of the beam with which the inspectionobject is irradiated. For example, the incident angle of the beam withwhich the inspection object is irradiated is controlled to be madenormal. Thus, the inspection of irregularities in a surface of aninspection object can be provided with high contrast and small foreignmatters (for example, foreign matters of 30 nm in size) can be detected.

Also, in the inspection apparatus, the image processing system mayinclude shading correction means that provides a shading correction thatuses a correcting white image and a correcting black image to an imageformed under the aperture imaging condition, and the correcting whiteimage may be created by adding a predetermined gradation value to theimage and the correcting black image may be created by subtracting apredetermined gradation value from the image.

Accordingly, the shading correction that uses the correcting white imageand the correcting black image is provided to the image formed under theaperture imaging condition. In such a situation, the correcting whiteimage is created by adding the predetermined gradation value (forexample, 40 gradations) to the image and the correcting black image iscreated by subtracting the predetermined gradation value (for example,40 gradations) from the image. A width between the gradation values ofthe correcting white image and the correcting black image is made small,so that irregularities (defects) of the inspection object can beemphasized. Therefore, smaller foreign matters (for example, foreignmatters of 20 nm in size) can be detected.

The inspection of irregularities in a surface of an inspection objectcan be provided with high contrast.

EMBODIMENTS

Referring to the drawings, embodiments will hereinafter be described ona semiconductor inspection apparatus that inspects a substrate, or awafer, on which a pattern is formed, as an inspection object. Note thatthe following embodiments are examples of an inspection apparatus and aninspection method.

FIGS. 1 and 2A respectively show an elevational view and a plan view ofmain configuration components of a semiconductor inspection apparatus 1of this embodiment.

The semiconductor inspection apparatus 1 of this embodiment includes: acassette holder 10 that holds a cassette storing multiple wafers; amini-environment device 20; a main housing 30 that defines a workingchamber; a loader housing 40 that is disposed between themini-environment device 20 and the main housing 30 to define two loadingchambers; a loader 60 that loads a wafer from the cassette holder 10onto a stage device 50 disposed in the main housing 30; an electronicoptical device 70 attached to a vacuum housing; an optical microscope3000; and a scanning electron microscope (SEM) 3002. These componentsare disposed in a positional relationship as shown in FIGS. 1 and 2A.The semiconductor inspection apparatus 1 further includes: a prechargeunit 81 disposed in the vacuum main housing 30; a potential applicationmechanism 83 (shown in FIG. 14) that applies a potential to a wafer; anelectron beam calibration mechanism 85; and an optical microscope 871that configures an alignment controller 87 for positioning the wafer onthe stage device. The electronic optical device 70 includes a lens tube71 and a light source tube 7000. The internal configuration of theelectronic optical device 70 will be described later.

Cassette Holder

The cassette holder 10 holds a plurality of (two in this embodiment)cassettes c (e.g., closed cassettes, such as SMIF and FOUP, made byAsyst technologies Inc.) each of which stores a plurality of (e.g., 25)wafers in a state of being arranged in the vertical direction inhorizontal orientation. In the case of conveying the cassette by a robotor the like and automatically loading the cassette to the cassetteholder 10, a cassette holder suitable to this loading manner is adopted.In the case of manual loading, a cassette holder that has an opencassette structure suitable to this loading manner is adopted. Any ofthe holders can be selected and installed. In this embodiment, thecassette holder 10 is in conformity with a system of automaticallyloading the cassette c, and includes, for instance, a lifting table 11,and a lifting mechanism 12 that vertically lifts and lowers the liftingtable 11. The cassette c can be automatically set onto the lifting tablein a state indicated by a chain line in FIG. 2A. After the setting, thecassette is automatically turned to a state indicated by a solid line inFIG. 2A to be aligned with the turning axis of a first conveyance unitin the mini-environment device. The lifting table 11 is lowered to astate indicated by a chain line in FIG. 1. Thus, the cassette holderused in the case of automatic loading or the cassette holder used in thecase of manual loading may be appropriately selected among cassetteshaving publicly known structures. Accordingly, detailed description onthe structure and functions of the cassette holder is omitted.

In another embodiment, as shown in FIG. 2B, a plurality of 300 mmsubstrates are stored in groove pockets (not shown) fixed in a box mainbody 501 in a state of being accommodated, and then conveyed or stored.The substrate conveyance box 24 includes: a box main body 501 having ashape of a rectangular cylinder; a substrate conveyance door 502 that isconnected to the box main body 501 and a device of automatically openingand closing the substrate conveyance door and can mechanically open andclose an opening on a side of the box main body 501; a cover 503 that isdisposed opposite to the opening and covers the opening through whichfilters and a fan motor is attached and detached; groove pockets (notshown) for storing substrates W; an ULPA filter 505; a chemical filter506; and a fan motor 507. In this embodiment, the substrate is carriedin and out by a robotic first conveyance unit 612 of the loader 60.

The substrates, or wafers, stored in the cassette c are to be inspected.The inspection is performed after or in a process on a wafer, insemiconductor manufacturing processes. More specifically, substrates,which are wafers, subjected to a film forming process, CMP, ioninjection, etc., wafers on which wiring patterns are formed, or waferson which wiring patterns have not been formed yet, are stored in thecassette. The wafers stored in the cassette c are arranged verticallyseparated and in parallel with each other. Accordingly, an arm of theafter-mentioned first conveyance unit is configured to be verticallymoved so as to hold the wafer at any position by the first conveyanceunit.

Mini-Environment Apparatus

In FIGS. 1 to 3, the mini-environment device 20 includes: a housing 22that defines an atmosphere-controlled mini-environment space 21; a gascirculator 23 that circulates gas, such as cleaned air, to control anatmosphere in the mini-environment space 21; an evacuator 24 thatcollects and evacuates a part of air supplied in the mini-environmentspace 21; and a prealigner 25 that is disposed in the mini-environmentspace 21 and roughly positions a substrate as an inspection object,i.e., a wafer.

The housing 22 includes a top wall 221, a bottom wall 222, andsurrounding walls 223 that surround the periphery, and thus has astructure that isolates the mini-environment space 21 from the outside.As shown in FIG. 3, in order to control the atmosphere in themini-environment space, the gas circulator 23 includes: a gas supplyunit 231 that is attached to the top wall 221 in the mini-environmentspace 21, cleans the gas (air in this embodiment), and flows the cleanedair as a laminar flow directly downward through one or more gas outlet(not shown); a collection duct 232 that is disposed on the bottom wall222 in the mini-environment space, and collects the air having flowndown toward the bottom; and a pipe 233 that communicates with thecollection duct 232 and the gas supply unit 231, and returns thecollected air to the gas supply unit 231. In this embodiment, the gassupply unit 231 captures about 20% of the air to be supplied, from theoutside of the housing 22 and cleans the captured air. However, theratio of the air captured from the outside is arbitrarily selected. Thegas supply unit 231 includes a HEPA or ULPA filter that has a publiclyknown structure for creating cleaned air. The downward laminar flow ofthe cleaned air, i.e., the downflow, is supplied mainly so as to flowover a conveyance surface of the after-mentioned first conveyance unitdisposed in the mini-environment space 21. The flow prevents dust thatmay possibly be caused by the conveyance unit from adhering to thewafer. Accordingly, the downflow nozzle is not necessarily disposed at aposition near the top wall as shown in the figure. The nozzle may bedisposed at any position above the conveyance surface of the conveyanceunit. The air is not necessarily flown over the entire surface of themini-environment space. In some cases, an ion wind is used as thecleaned air to secure cleanness. A sensor for observing the cleannessmay be provided in the mini-environment space, and the apparatus can beshut down when the cleanness is degraded. A gateway 225 is formed at aportion of the surrounding wall 223 of the housing 22 that is adjacentto the cassette holder 10. A shutter device having a publicly knownstructure may be provided adjacent to the gateway 225 to shut thegateway 225 from a side of the mini-environment device. The downflow ofthe laminar flow formed adjacent to the wafer may have, for instance, aflow rate of 0.3 to 0.4 m/sec. The gas supply unit may be providedoutside of the mini-environment space, instead of the inside of thisspace.

The evacuator 24 includes: an intake duct 241 disposed at a positionbelow a wafer conveyance surface of the conveyance unit, at a lower partof the conveyance unit; a blower 242 disposed outside of the housing 22;and a pipe 243 that communicates with the intake duct 241 and the blower242. The evacuator 24 sucks, into intake duct 241, the gas that flowsaround the conveyance unit and may contain dust that may possibly becaused by the conveyance unit, and evacuates the gas out of the housing22 through the pipes 243 and 244 and the blower 242. In this case, thegas may be evacuated into an exhaust pipe (not shown) drawn adjacent tothe housing 22.

The aligner 25 disposed in the mini-environment space 21 optically ormechanically detects an orientation flat (a flat part formed at thecircumference of the circular wafer) formed at the wafer or one or moreV-shaped notches formed at the circumference of the wafer, andpreliminarily positions the wafer in the turning direction about theaxis O-O of the wafer at an accuracy of about ±1 degree. The prealignerconfigures a part of a mechanism of determining the coordinates of aninspection object, and functions to roughly position the inspectionobject. The prealigner itself may be a prealigner having a publiclyknown structure. Accordingly, description on the structure andoperations is omitted.

Although not shown, a collection duct for the evacuator may be providedalso at the lower part of the prealigner to evacuate air including dustejected from the prealigner to the outside.

Main Housing

In FIGS. 1 and 2A, the main housing 30, which defines a working chamber31, includes a housing main body 32. The housing main body 32 issupported by a housing supporter 33 mounted on a vibration isolatingdevice, or a vibration isolator 37, disposed on a base frame 36. Thehousing supporter 33 includes a frame structure 331 configured into arectangular shape. The housing main body 32, which is disposed and fixedonto the frame structure 331, includes a bottom wall 321 mounted on theframe structure, a top wall 322, surrounding walls 323 that areconnected to the bottom wall 321 and the top wall 322 and surround theperiphery, and isolates the working chamber 31 from the outside. In thisembodiment, the bottom wall 321 is made of steel plates having arelatively large thickness not to cause distortion due to the weight ofa device, such as a stage device, mounted on this wall. However, thebottom wall may have another structure. In this embodiment, the housingmain body and the housing supporter 33 are configured to have rigidstructures. The configuration allows the vibration isolator 37 toprevent vibrations of a floor on which the base frame 36 is installedfrom being transferred to the rigid structures. A gateway 325 throughwhich a wafer is carried in and out is formed at a surrounding walladjacent to the after-mentioned loader housing among the surroundingwalls 323 of the housing main body 32.

The vibration isolator may be an active isolator having an air spring, amagnetic bearing or the like, or a passive isolator including thesecomponents. Each of the isolators may be an isolator having a publiclyknown structure. Accordingly, description on the structure andoperations is omitted. The atmosphere in the working chamber 31 is keptin a vacuum atmosphere by a vacuum device (not shown) having a publiclyknown structure. A controller 2 that controls the operations of theentire apparatus is disposed at the bottom of the base frame 36.

Loader Housing

In FIGS. 1, 2A and 4, the loader housing 40 includes a housing main body43 that defines a first loading chamber 41 and a second loading chamber42. The housing main body 43 includes a bottom wall 431, a top wall 432,surrounding walls 433 that surround the periphery, and a partition wall434 that separates the first loading chamber 41 and the second loadingchamber 42 from each other. The structure can separate both the loadingchambers from the outside. An opening, or a gateway 435, through which awafer is exchanged between both the loading chambers is formed at thepartition wall 434. Gateways 436 and 437 are formed at portions of thesurrounding walls 433 adjacent to the mini-environment device and themain housing. The housing main body 43 of the loader housing 40 ismounted on the frame structure 331 of the housing supporter 33, andsupported by this structure. Accordingly, vibrations of the floor arenot transmitted to loader housing 40 either. The gateway 436 of theloader housing 40 and the gateway 226 of the housing 22 of themini-environment device match with each other. A shutter device 27 thatselectively blocks communication between the mini-environment space 21and the first loading chamber 41 is provided at the matching portion.The shutter device 27 includes: a seal member 271 that surrounds thegateways 226 and 436 and is in close contact with and fixed to the sidewall 433; a door 272 cooperates with the seal member 271 to prevent theair from flowing through the gateways; and a drive device 273 that movesthe door. The gateway 437 of the loader housing 40 and the gateway 325of the housing main body 32 match with each other. A shutter device 45is provided that selectively blocks communication between the secondloading chamber 42 and the working chamber 31. The shutter device 45includes: a seal member 451 that surrounds the gateways 437 and 325 andis in close contact with and fixed to the respective side walls 433 and323; a door 452 that cooperates with seal member 451 to blockcommunication of air through the gateways; and a drive device 453 thatmoves the door. Furthermore, a shutter device 46 that closes the door461 to selectively seal and block communication between the first andsecond loading chambers is provided at an opening formed at thepartition wall 434. In closed states, the shutter devices 27, 45 and 46can hermetically seal the corresponding chambers. These shutter devicesmay be devices having a publicly known structure. Accordingly, detaileddescription on the structure and operations is omitted. The method ofsupporting the housing 22 of the mini-environment device 20 is differentfrom the method of supporting the loader housing. In order to preventvibrations of the floor from being transmitted to the loader housing 40and the main housing 30 through the mini-environment device, a vibrationisolating cushion member is preferably disposed between the housing 22and the loader housing 40 so as to hermetically surround the gateway.

A wafer rack 47 that vertically separates a plurality of (two in thisembodiment) wafers and horizontally supports the wafers is arranged inthe first loading chamber 41. As shown in FIGS. 5A and 5B, the waferrack 47 includes pillars 472 fixed in a manner of being separated at thefour corners of a rectangular substrate 471 in a state of standingupright. Two stages of supporters 473 and 474 are formed at each pillar472. The periphery of the wafer W is mounted on the supporters, and thusthe wafer is held. The distal ends of the arms of the after-mentionedfirst and second conveyance units are moved to approach the wafersbetween the adjacent pillars, and the arms hold the wafers.

The atmospheres of the loading chambers 41 and 42 can be controlled to ahigh vacuum (a degree of vacuum of 10⁻³ to 10⁻⁶ Pa) by a vacuumevacuator (not shown) that has a publicly known structure including avacuum pump (not shown). In this case, the first loading chamber 41 maybe kept in a low vacuum atmosphere and serve as a low vacuum chamber,and the second loading chamber 42 may be kept in a high vacuumatmosphere and serve as a high vacuum chamber. This structure canefficiently prevent wafer from being contaminated. Adoption of thestructure can convey a wafer that is stored in the loading chamber andto be subjected to defect inspection at the next time, into the workingchamber without delay. Adoption of such a loading chamber can improvethe throughput of defect inspection, and achieve a degree of vacuum ashigh as possible around an electron source, which is required to bestored in a high vacuum state.

A vacuum exhaust pipe and a vent pipe for inert gas (e.g., dry purenitrogen) (both the pipes are not shown) communicate to first and secondloading chambers 41 and 42, respectively. According to thisconfiguration, an atmospheric pressure state in each loading chamber canbe achieved by the inert gas vent (inert gas is injected to preventoxygen gas etc. other than inert gas from adhering to the surface). Thedevice for such inert gas venting may be a device having a publiclyknown structure. Accordingly, the detailed description is omitted.

Stage Device

The stage device 50 includes: a fixed table 51 disposed on the bottomwall 321 of the main housing 30; a Y table 52 that moves in the Ydirection (the direction perpendicular to the sheet of FIG. 1) on thefixed table; an X table 53 that moves in the X direction (the lateraldirection in FIG. 1) on the Y table; a turn table 54 that can turn onthe X table; and a holder 55 disposed on the turn table 54. A wafer isreleasably held on a wafer-mounting surface 551 of the holder 55. Theholder may be a holder that has a publicly known structure and canreleasably grip a wafer mechanically or according to an electrostaticchuck system. The stage device 50 can highly accurately position a waferheld by the holder on the mounting surface 551, in the X direction, Ydirection and the Z direction (the vertical direction in FIG. 1), andfurther in a direction (θ direction) about an axis perpendicular to thewafer holding surface, with respect to an electron beam emitted from theelectronic optical device, by moving the tables using servomotors,encoders and various sensors (not shown). As to the positioning in the Zdirection, for instance, the position of the mounting surface on theholder may preferably be slightly adjusted in the Z direction. In thiscase, the reference position of the mounting surface is detected by aposition measuring instrument using fine diameter laser (a laserinterferometric distance meter adopting the principle of aninterferometer), and the position is controlled by a feedback circuit,not shown. Together with or instead of this control, the position of thenotch or the orientation flat of the wafer is measured to detect theplanar position and the turning position of the wafer with respect tothe electron beam, and the positions are controlled by turning the turntable by a stepping motor or the like capable of fine angle control. Inorder to prevent dust from occurring in the working chamber as much aspossible, servomotors 521 and 531 and encoders 522 and 532 for the stagedevice are disposed out of the main housing 30. The stage device 50 maybe, for instance, a device used in a stepper or the like having apublicly known structure. Accordingly, detailed description on thestructure and operations is omitted. The laser interferometric distancemeter may be a meter having a publicly known structure. Accordingly,detailed description on the structure and operations is omitted.

The wafer turning position and the X and Y positions with respect to theelectron beam are preliminarily input into an after-mentioned signaldetection system or an image processing system to allow the signal to bestandardized. Furthermore, a wafer chuck mechanism provided in theholder can apply a voltage for chucking a wafer to an electrode of anelectrostatic chuck, and press three points on the circumference of thewafer (the points preferably separated by regular intervals in thecircumferential direction) for positioning. The wafer chuck mechanismincludes two fixed positioning pins, and one pressing crank pin. Theclamp pin can achieve automatic chucking and automatic releasing, andconfigures a conduct part for voltage application.

In this embodiment, the table moving in the lateral direction in FIG. 2Ais the X table, and the table moving in the vertical direction is the Ytable. Instead, the table moving in the lateral direction may be the Ytable, and the table moving in the vertical direction may be the X tablein this diagram.

Loader

The loader 60 includes: a robotic first conveyance unit 61 disposed inthe housing 22 of the mini-environment device 20; and a robotic secondconveyance unit 63 disposed in the second loading chamber 42.

The first conveyance unit 61 includes a multi-axial arm 612 capable ofturning about an axis O₁-O₁ with respect to a driver 611. Themulti-axial arm may be an arm having any configuration. In thisembodiment, the arm includes three parts attached in a manner capable ofturning with respect to each other. A part of the arm 612 of the firstconveyance unit 61, i.e., a first part nearest the driver 611, isattached to a shaft 613 that can be turned by a drive mechanism (notshown) that has a publicly known structure and provided in the driver611. The arm 612 can be turned about the axis O₁-O₁ by the shaft 613,and extend and contract in the radial direction with respect to the axisO₁-O₁ as a whole by relative turning between the components. A distalend of a third part of the arm 612 that is most opposite to the shaft613 is provided with a grip device 616 that has a publicly knownstructure, such as a mechanical chuck or electrostatic chuck, and gripsa wafer. The driver 611 can be vertically moved by a lifting mechanism615 having a publicly known structure.

The first conveyance unit 61 extends the arm 612 toward any one ofdirections M1 and M2 of the two cassettes c held by the cassette holder,mounts one wafer stored in the cassette c on the arm or grips the waferusing a chuck (not shown) attached to the distal end of the arm, andpicks up the wafer. Subsequently, the arm is contracted (a state shownin FIG. 2A), turns to a position allowing the arm to extend in adirection M3 of the prealigner 25, and stops at this position. The armthen extends again, and mounts the wafer held by the arm on theprealigner 25. After the wafer is received from the prealigner in amanner inverted from the above description, the arm further turns andstops at a position allowing the arm to extend toward the second loadingchamber 41 (direction M4), and exchanges the wafer with the wafer rack47 in the second loading chamber 41. In the case of mechanicallygripping the wafer, the peripheral portion of the wafer (a range withinabout 5 mm from the periphery) is grasped. This gripping manner isadopted because a device (circuit wiring) is formed on the entiresurface except for the peripheral part of the wafer and gripping of thisportion breaks the device and causes a defect.

The second conveyance unit 63 has a structure basically identical to thestructure of the first conveyance unit. The structure is different onlyin that the wafer is conveyed between the wafer rack 47 and the mountingsurface of the stage device. Accordingly, the detailed description isomitted.

In the loader 60, the first and second conveyance units 61 and 63 conveya wafer from the cassette held in the cassette holder onto the stagedevice 50 disposed in the working chamber 31 and convey a wafer in theinverse direction, in a state where the wafer is maintained in ahorizontal orientation. The arm of the conveyance unit vertically movesonly in the cases where the wafer is picked up from and inserted intothe cassette, the wafer is mounted on and picked up from the wafer rack,and the wafer is mounted on and picked up from the storage device.Accordingly, even a large wafer, e.g., a wafer having a diameter of 30cm, can be smoothly moved.

Wafer Conveyance

Next, conveyance of a wafer from the cassette c supported by thecassette holder to the stage device 50 disposed in the working chamber31 will be sequentially described.

In the case of manually setting the cassette, the cassette holder 10 maybe a holder having a structure suitable to the setting manner. In thecase of automatically setting the cassette, the cassette holder 10 maybe a holder having a structure suitable to the setting manner. In thisembodiment, after the cassette c is set on the lifting table 11 of thecassette holder 10, the lifting table 11 is lowered by the liftingmechanism 12 to match the cassette c with the gateway 225.

After the cassette matches with the gateway 225, a cover (not shown)provided on the cassette opens. Furthermore, a cylindrical cover isdisposed between the cassette c and the gateway 225 of themini-environment. The configuration isolates the insides of the cassetteand the mini-environment space from the outside. These structures arepublicly known. Accordingly, detailed description on the structures andoperations is omitted. In the case where a shutter device that opens andcloses the gateway 225 is provided on the mini-environment device 20,the shutter device operates to open the gateway 225.

Meanwhile, the arm 612 of the first conveyance unit 61 stops in any ofstates of orientations in the directions M1 and M2 (the direction M1 inthis direction). After the gateway 225 opens, the arm extends andreceives one of the wafers stored in the cassette at the distal end ofthe arm. The vertical positions of the arm and the wafer to be picked upfrom the cassette are adjusted by vertically moving the driver 611 andthe arm 612 of the first conveyance unit 61 in this embodiment. Instead,the movement may be achieved by vertically moving the lifting table ofthe cassette holder. Both movements may be adopted.

After the arm 612 has received the wafer, the arm is contracted. Thegateway is closed by operating the shutter device (in the case with theshutter device). Next, the arm 612 comes into a state capable ofextending in the direction M3 by turning about the axis O₁-O₁. The armthen extends and mounts, on the prealigner 25, the wafer mounted on thedistal end of the arm or gripped by the chuck. The prealigner positionsthe orientation of the wafer in the turning direction (the directionabout a central axis perpendicular to the wafer surface) within aprescribed range. After the positioning has been completed, theconveyance unit 61 receives the wafer from the prealigner 25 at thedistal end of the arm and subsequently the arm is contracted to have anorientation allowing the arm to extend toward in the direction M4. Thedoor 272 of the shutter device 27 then operates to open the gateways 226and 436, the arm 612 extends to mount the wafer on the upper stage orthe lower stage of the wafer rack 47 in the first loading chamber 41. Asdescribed above, before the shutter device 27 opens and the wafer iscarried into the wafer rack 47, the opening 435 formed at the partitionwall 434 is hermetically closed by the door 461 of the shutter device46.

In the process of conveying the wafer by the first conveyance unit,cleaned air flows as a laminar flow (as a downflow) from the gas supplyunit 231 provided on the housing of the mini-environment device. Theflow prevents dust from adhering to the upper surface of the waferduring conveyance. A part of air around the conveyance unit (about 20%of air that is supplied from a supply unit and mainly dirty in thisembodiment) is sucked from the intake duct 241 of the evacuator 24 andevacuated out of the housing. The remaining air is collected through thecollection duct 232 provided at the bottom of the housing, and returnedto the gas supply unit 231 again.

After the wafer is mounted in the wafer rack 47 in the first loadingchamber 41 of the loader housing 40 by the first conveyance unit 61, theshutter device 27 is closed to seal the inside of the loading chamber41. The inert gas is then charged in the first loading chamber 41 toevacuate the air, and subsequently the inert gas is also evacuated. Theinside of the loading chamber 41 is thus in a vacuum atmosphere. Thevacuum atmosphere of the first loading chamber may be a low degree ofvacuum. After a certain degree of vacuum is achieved in the loadingchamber 41, the shutter device 46 operates to open the gateway 434having being hermetically closed with the door 461, the arm 632 of thesecond conveyance unit 63 extends, and receives one wafer from the waferrack 47 by the grip device at the distal end (mounted on the distal endor gripped by the chuck attached to the distal end). After the wafer hasbeen received, the arm is contracted, the shutter device 46 operatesagain, and the gateway 435 is closed with the door 461. Before theshutter device 46 opens, the arm 632 preliminarily becomes in anorientation capable of extending in the direction N1 toward the waferrack 47. As described above, before the shutter device 46 opens, thegateways 437 and 325 are closed with the door 452 of the shutter device45, communication between the insides of the second loading chamber 42and the working chamber 31 is blocked in a hermetical state, and theinside of the second loading chamber 42 is vacuum-evacuated.

After the shutter device 46 closes the gateway 435, the inside of thesecond loading chamber is vacuum-evacuated again to be in a degree ofvacuum higher than the degree in the first loading chamber. Meanwhile,the arm of the second conveyance unit 61 turns to a position capable ofextending in the direction toward the stage device 50 in the workingchamber 31. On the other hand, in the stage device in the workingchamber 31, the Y table 52 moves upward in FIG. 2A to a position wherethe center line X₀-X₀ of the X table 53 substantially matches with the Xaxis X₁-X₁ crossing the turning axis O₂-O₂ of the second conveyance unit63. The X table 53 moves to a position approaching the left-mostposition in FIG. 2A. The tables are thus in a waiting state. When thesecond loading chamber becomes a state substantially identical to avacuum state in the working chamber, the door 452 of the shutter device45 operates to open the gateways 437 and 325, the arm extends, and thusthe distal end of the arm holding the wafer approaches the stage devicein the working chamber 31. The wafer is mounted on the mounting surface551 of the stage device 50. After the wafer has been mounted, the arm iscontracted, and the shutter device 45 closes the gateways 437 and 325.

The operations of conveying the wafer in the cassette c onto the stagedevice has been described above. However, the wafer mounted on the stagedevice and in a state where the processes have been completed isreturned from the stage device to the cassette c according to invertedoperations with respect to the aforementioned operations. Since themultiple wafers are mounted on the wafer rack 47, a wafer can beconveyed between the cassette and the wafer rack by the first conveyanceunit during conveyance of a wafer between the wafer rack and the stagedevice by the second conveyance unit. Accordingly, the inspectionprocess can be efficiently performed.

More specifically, in the case where a processed wafer A and anunprocessed wafer B are on the wafer rack 47 of the second conveyanceunit,

(1) first, the unprocessed wafer B is moved to the stage device 50, andthe process is started, and (2) during the process, the processed waferA is moved by the arm from the stage device 50 to the wafer rack 47, andthe unprocessed wafer C is picked up from the wafer rack also by thearm, positioned by the prealigner, and subsequently moved to the waferrack 47 of the loading chamber 41.

Thus, in the wafer rack 47, during the process on the wafer B, theprocessed wafer A can be replaced with the unprocessed wafer C.

According to certain usage of such an apparatus performing inspection orevaluation, multiple stage devices 50 may be arranged in parallel, andthe wafer may be moved from one wafer rack 47 to each apparatus, therebyallowing multiple wafers to be subjected to the same process.

FIG. 6 shows a variation of a method of supporting a main housing. Inthe variation shown in FIG. 6, the housing supporter 33 a includes asteel plate 331 a that is thick and rectangular. A housing main body 32a is mounted on the steel plate. Accordingly, a bottom wall 321 a of thehousing main body 32 a has a thinner structure than the bottom wall ofthe aforementioned embodiment. In a variation shown in FIG. 7, a housingmain body 32 b and a loader housing 40 b are suspended and supported bya frame structure 336 b of a housing supporter 33 b. The bottom ends ofmultiple vertical frames 337 b fixed to the frame structure 336 b arefixed to the four corners of the bottom wall 321 b of the housing mainbody 32 b. The bottom wall supports surrounding walls and a top wall.Vibration isolators 37 b are disposed between the frame structure 336 band the base frame 36 b. The loader housing 40 is also suspended by asupporting member 49 b fixed to the frame structure 336. In thevariation of the housing main body 32 b shown in FIG. 7, the support isachieved by suspension. Accordingly, in this variation, the centers ofgravity of the main housing and all the devices provided in this housingcan be lowered. The method of supporting the main housing and the loaderhousing, which includes the variations, prevents vibrations of the floorfrom being transmitted to the main housing and the loader housing.

In another variation, not shown, only the housing main body of the mainhousing may be supported by a housing supporting device from the lowerside, and the loader housing may be disposed on the floor according tothe same method as of the adjacent mini-environment device. In a stillanother variation, not shown, only the housing main body of the mainhousing may be supported by the frame structure in a suspending manner,and the loader housing may be disposed on the floor according to thesame method as of the adjacent mini-environment device.

The embodiments can exert the following advantageous effects.

(A) The entire configuration of the mapping projection inspectionapparatus that uses an electron beam can be acquired, and inspectionobjects can be processed at high throughput.

(B) In the mini-environment space, cleaned gas flows around theinspection object to prevent dust from adhering, and the sensorsobserving cleanness are provided. Thus, the inspection object can beinspected while dust in the space is monitored.

(C) The loading chamber and the working chamber are integrally supportedvia the vibration isolation device. Accordingly, the inspection objectcan be supplied to the stage device and inspected without being affectedby the external environment.

Electronic Optical Device

The electronic optical device 70 includes the lens tube 71 fixed to thehousing main body 32. This tube internally includes: an optical systemincluding a primary light source optical system (hereinafter, simplyreferred to as “primary optical system”) 72 and a secondary electronicoptical system (hereinafter, simply referred to as “secondary opticalsystem”) 74; and a detection system 76. FIG. 8 is a schematic diagramshowing an overview of a configuration of a “light irradiation type”electronic optical device. In the electronic optical device (lightirradiation electronic optical device) in FIG. 8, a primary opticalsystem 72, which is an optical system irradiating a surface of a wafer Was an inspection object with a light beam, includes a light source 10000that emits the light beam, and a mirror 10001 that changes the directionof the light beam. In the light irradiation electronic optical device,the optical axis of the light beam 10000A emitted from the light sourceis inclined from the optical axis (perpendicular to the surface of thewafer W) of photoelectrons emitted from the wafer W, which is theinspection object.

The detection system 76 includes a detector 761 disposed on an imagingsurface of a lens system 741, and an image processor 763.

Light Source (Light Beam Source)

In the electronic optical device in FIG. 8, a DUV laser light source isadopted as a light source 10000. The DUV laser light source 10000 emitsDUV laser light. Another light source may be adopted that allowsphotoelectrons to emit from a substrate irradiated with light from thelight source 10000, such as UV, DUV, and EUV light and laser, X-rays andX-ray laser.

Primary Optical System

An optical system where a light beam emitted from the light source 10000forms a primary light beam, with which a surface of the wafer W isirradiated, forming a rectangular or circular (or elliptical) beam spot,is referred to as a primary optical system. The light beam emitted fromthe light source 10000 passes through an objective lens optical system724, and the light beam serves as the primary light beam with which thewafer WF on the stage device 50 is irradiated.

Secondary Optical System

A two-dimensional image of photoelectrons caused by the light beam withwhich the wafer W is irradiated passes through a hole formed at themirror 10001, is formed at a field stop position by electrostatic lenses(transfer lenses) 10006 and 10009 through a numerical aperture 10008,enlarged and projected by a lens 741 thereafter, and detected by thedetection system 76. The image-forming projection optical system isreferred to as a secondary optical system 74.

Here, a minus bias voltage is applied to the wafer. The difference ofpotentials between the electrostatic lens 724 (lenses 724-1 and 724-2)and the wafer accelerates the photoelectrons caused on the surface ofthe sample to exert an advantageous effect of reducing chromaticaberration. An extracted electric field in the objective lens opticalsystem 724 is 3 to 10 kV/mm, which is a high electric field. There is arelationship where increase in extracted electric field exertsadvantageous effects of reducing aberrations and improving resolution.Meanwhile, increase in extracted electric field increases voltagegradient, which facilitates occurrence of evacuated. Accordingly, it isimportant to select and use an appropriate value of the extractedelectric field. Electrons enlarged to a prescribed magnification by thelens 724 (CL) is converged by the lens (TL1) 10006, and forms acrossover (CO) on the numerical aperture 10008 (NA). The combination ofthe lens (TL1) 10006 and the lens (TL2) 10009 can zoom themagnification. Subsequently, the enlarged projection is performed by thelens (PL) 741, and an image is formed on an MCP (micro channel plate) onthe detector 761. In this optical system, NA is disposed betweenTL1-TL2. The system is optimized to configure an optical system capableof reducing off-axis aberrations.

Detector

A photoelectronic image from the wafer to be formed by the secondaryoptical system is amplified by the micro channel plate (MCP),subsequently collides with a fluorescent screen and converted into anoptical image. According to the principle of the MCP, a prescribedvoltage is applied using a hundred of significantly fine, conductiveglass capillaries that are bundled to have a diameter 6 to 25 μm and alength of 0.24 to 1.0 mm and formed into a shape of a thin plate,thereby allowing each of the capillaries to function as independentelectronic amplifier; the entire capillaries thus form an integratedelectronic amplifier.

The image converted into light by the detector is projected on a TDI(time delay integration)-CCD (charge coupled device) by an FOP (fiberoptical plate) system disposed in the atmosphere through a vacuumtransmissive window in one-to-one mapping. According to anotherprojection method, the FOP coated with fluorescent material is connectedto the surface of a TDI sensor, and a signal electronically/opticallyconverted in a vacuum may be introduced into the TDI sensor. This casehas a more efficient transmittance and efficiency of an MTF (modulationtransfer function) than the case of being arranged in the atmospherehas. For instance, the transmittance and MTF can be high values of ×5 to×10. Here, the combination of the MCP and TDI may be adopted as thedetector as described above. Instead, an EB (electron bombardment)-TDIor an EB-CCD may be adopted. In the case of adopting the EB-TDI,photoelectrons caused on the surface of the sample and forming atwo-dimensional image is directly incident onto the surface of theEB-TDI sensor. Accordingly, an image signal can be formed withoutdegradation in resolution. For instance, in the case of the combinationof the MCP and TDI, electronic amplification is performed by the MCP,and electronic/optical conversion is performed by fluorescent materialor a scintillator, and information on the optical image is delivered tothe TDI sensor. In contrast, the EB-TDI and the EB-CCD have no componentfor electronic/optical conversion and no transmission component foroptical amplification information and thus have no loss due to thecomponent. Accordingly, a signal can be transmitted to the sensorwithout image degradation. For instance, in the case of adopting thecombination of the MCP and TDI, the MTF and contrast are ½ to ⅓ of theMTF and contrast in the cases of adopting the EB-TDI and the EB-CCD.

In this embodiment, it is provided that a high voltage of 10 to 50 kV isapplied to the objective lens system 724, and the wafer W is arranged.

Description on Relationship of Main Functions of Mapping ProjectionSystem and Overview

FIG. 9 is a diagram showing the entire configuration of this embodiment.However, certain parts of components are abbreviated in the diagram.

In FIG. 9, the inspection apparatus includes the lens tube 71, a lightsource tube 7000, and a chamber 32. The light source 10000 is providedin the light source tube 7000. The primary optical system 72 is disposedon the optical axis of a light beam (primary light beam) emitted fromthe light source 10000. The stage device 50 is installed in the chamber32. The wafer W is mounted on the stage device 50.

Meanwhile, the cathode lens 724 (724-1 and 724-2), the transfer lenses10006 and 10009, the numerical aperture (NA) 10008, the lens 741 and thedetector 761 are disposed on the optical axis of a secondary beamemitted from the wafer W, in the lens tube 71. The numerical aperture(NA) 10008 corresponds to an aperture stop, and is a thin plate that ismade of metal (Mo. etc.) and has a circular hole.

The output of the detector 761 is input into a control unit 780. Theoutput of the control unit 780 is input into a CPU 781. Control signalsof the CPU 781 are input into a light source control unit 71 a, a lenstube control unit 71 b and a stage driving mechanism 56. The lightsource control unit 71 a controls power supply to the light source10000. The lens tube control unit 71 b controls the lens voltages of thecathode lens 724, the lenses 10006 and 10009, and the lens 741, and thevoltage of an aligner (not shown) (control of deflection).

The stage driving mechanism 56 transmits position information of thestage to the CPU 781. The light source tube 7000, the lens tube 71, andthe chamber 32 communicate with a vacuum evacuation system (not shown).Air in the vacuum evacuation system is evacuated by a turbo pump of thevacuum evacuation system, and the inside of the chamber is kept in avacuum. A rough evacuation system that typically adopts a dry pump or arotary pump is disposed on a downstream side of the turbo pump.

When the sample is irradiated with the primary light beam,photoelectrons occur as the secondary beam from the surface of the waferW irradiated with the light beam.

The secondary beam passes through the cathode lens 724, the group of TLlenses 10006 and 10009 and the lens (PL) 741, and is guided to thedetector and formed as an image.

The cathode lens 724 includes three electrodes. It is designed such thatthe lowermost electrode forms a positive electric field with respect tothe potential on the side of the sample W, and electrons (morespecifically, secondary electrons having a small directivity) areextracted and efficiently guided into the lens. Thus, it is effectivethat the cathode lens is bi-telecentric. The secondary beam image-formedby the cathode lens passes through the hole of the mirror 10001.

If the secondary beam is image-formed by only one stage of the cathodelens 724, the effect of the lens is too strong. Accordingly, aberrationeasily occurs. Thus, the two stages of the doublet lens system areadopted for a formation of an image. In this case, the intermediateimage formation position is between the lens (TL1) 10006 and the cathodelens 724. Here, as described above, the bi-telecentric configurationsignificantly exerts an advantageous effect of reducing the aberration.The secondary beam is converged on the numerical aperture (NA) 10008 bythe cathode lens 724 and the lens (TL1) 10006, thereby forming acrossover. The image is formed between the lens 724 and lens (TL1)10006. Subsequently, an intermediate magnification is defined by thelens (TL1) 10006 and the lens (TL2) 10009. The image is enlarged by thelens (PL) 741 and formed on the detector 761. That is, in this example,the image is formed three times as a total.

All the lenses 10006, 10009 and 741 are rotationally symmetrical lensesreferred to as unipotential lenses or einzel lenses. The lenses have aconfiguration including three electrodes. Typically, the external twoelectrodes are zero potential, and control is performed by applying avoltage to the central electrode to exert a lens effect. Theconfiguration is not limited to this lens configuration. Instead, thecase of a configuration including a focus adjustment electrode on thefirst or second stage or both the stages of the lens 724, the case ofincluding dynamic focus adjustment electrode and has a quadrupole orquintuple-pole configuration can be adopted. The field lens function maybe added to the PL lens 741 to reduce off-axis aberrations, and aquadrupole or quintuple-pole configuration may effectively be adopted toincrease the magnification.

The secondary beam is enlarged and projected by the secondary opticalsystem, and image-formed on the detection surface of the detector 761.The detector 761 includes: the MCP that amplitudes electrons; afluorescent plate that converts the electrons into light; a lens oranother optical element for relaying an optical image between the vacuumsystem and the outside; and an image pickup element (CCD etc.). Thesecondary beam is image-formed on the MCP detection surface, andamplified. The electrons are converted into an optical signal by thefluorescent plate, and further converted into a photoelectric signal byan image pickup element.

The control unit 780 reads the image signal of the wafer W from thedetector 761 and transmits the read signal to the CPU 781. The CPU 781inspects defect on a pattern based on the image signal according totemplate matching or the like. The stage device 50 is movable in the XYdirection by the stage driving mechanism 56. The CPU 781 reads theposition of the stage device 50, outputs a drive control signal to thestage driving mechanism 56 to drive the stage device 50, therebysequentially detecting and inspecting images.

As to change in magnification, even if a set magnification, which islens conditions of the lenses 10006 and 10009, is changed, a uniformimage can be acquired on the entire field of view on the detection side.In this embodiment, a uniform image without irregularity can beacquired. However, increase in magnification causes a problem ofdecreasing the brightness of the image. In order to solve the problem,the lens condition of the primary optical system is set such that theamount of emitted electrons per unit pixel is constant when the lenscondition of the secondary optical system is changed to change themagnification.

Precharge Unit

As shown in FIG. 1, the precharge unit 81 is arranged adjacent to thelens tube 71 of the electronic optical device 70 in the working chamber31. This inspection apparatus is an apparatus that inspects a devicepattern and the like formed on the surface of the wafer by irradiatingthe substrate as the inspection object, i.e., wafer, with the electronbeam. The information on the photoelectrons caused by irradiation withthe light beam is information on the surface of the wafer. However, thesurface of the wafer may be charged (charged up) according toconditions, such as a wafer material, the wavelength and energy ofirradiation light or laser. Furthermore, a strongly charged spot and aweakly charged spot may occur on the surface of the wafer. If there isirregularity of the amount of charge on the surface of the wafer, thephotoelectronic information also includes irregularity. Accordingly,correct information cannot be acquired. Thus, in this embodiment, toprevent the irregularity, the precharge unit 81 including a chargedparticles irradiation unit 811 is provided. Before a prescribed spot onthe wafer to be inspected is irradiated with light or laser, chargedparticles are emitted from the charged particles irradiation unit 811 ofthe precharge unit to eliminate charging irregularity. The charging-upon the surface of the wafer preliminarily forms an image of the surfaceof the wafer, which is a detection object. Detection is performed byevaluating the image to operate the precharge unit 81 on the basis ofthe detection.

Embodiment 1

Semiconductor Inspection Apparatus Including Double Pipe Structure LensTube

As described above, the electronic optical device 70 including theprimary optical system 2100, which is described as the second embodimentof the primary optical system, is different in setting of voltagesapplied to the respective configurational components from a typicalelectron gun. That is, reference potential V2 is used as the highvoltage (e.g., +40000 V). First, the semiconductor inspection apparatus1 including the electronic optical device 70 has a double pipestructure.

Description will be made with reference to FIG. 10. FIG. 10 is a diagramschematically showing the double pipe structure of the semiconductorinspection apparatus according to one embodiment. In FIG. 10, the firstpipe and the second pipe are emphasized. The sections of the actualfirst pipe and second pipe are different from the illustration. As shownin FIG. 10, the electronic optical device 70 including the primaryoptical system 2000 includes two pipes, which are the first pipe 10071,and a second pipe 10072 provided outside of the first pipe 10071. Inother words, the device has a double pipe structure. The double pipestructure internally stores a light source, a primary optical system, asecondary optical system and a detector. A high voltage (e.g., +40000 V)is applied to the first pipe 10071. The second pipe 10072 is set to GND.The first pipe 10071 secures a spatial reference potential V0 withreference to the high voltage. The first pipe is surrounded by thesecond pipe and is thus set to GND. This configuration achieves GNDconnection in the apparatus installation and prevents electric shock.The pipe 10071 is fixed to the pipe 10072 by insulative components. Thepipe 10072 is set to GND, and attached to the main housing 30. Theprimary optical system 2000, the secondary optical system, the detectionsystem 76 and the like are arranged in the first pipe 10071.

An internal partition wall between the first pipe 10071 and the secondpipe 10072, even including components screws and the like, are made ofnonmagnetic material not to affect the magnetic field, therebypreventing the magnetic field from affecting the electron beam. Althoughnot shown in FIG. 10, a space is provided at the side of the second pipe10072. In the space, a protrusion is connected in which parts of theprimary optical system 2000, such as the light source and thephotoelectron generator, are arranged. A space similar to the spaceprovided for the second pipe 10072 is also provided for the first pipe10071. Photoelectrons occurring from the photoelectron generationportion pass through the spaces, and the sample is irradiated with thephotoelectrons. The light source is not necessarily provided in thesecond pipe 10072. Instead, the light source may be provided on theatmosphere side, and light may be introduced into the photoelectrongeneration portion stored in the second pipe 10072 on the vacuum side.However, the primary optical system and the secondary optical system arenecessarily stored in the double pipe structure. The detector may bedisposed in the first pipe 10071, or at the position with a potentialindependent from the first and second pipes. Here, the potential of thedetection surface of the detector is set to any value to control theenergy of electrons incident on the detector to have an appropriatevalue. In a state of potential separation by the insulative componentfrom the pipe 1 and the pipe 2, any voltage is applied to the detectorto achieve a detection sensor surface potential, thereby allowingoperation. Here, provided that the sensor surface potential is VD, theenergy incident on the sensor surface is defined by VD-RTD. In the casewhere EB-CCD or EB-TDI is adopted as the detector, it is effective toset the incident energy to 1 to 7 keV for the sake of reducing damage tothe sensor and use for a long period of time.

Electronic Inspection Apparatus

FIG. 11 is a diagram showing a configuration of an electron beaminspection apparatus. The above description has been made mainly on theprinciple of the foreign matter inspection method. The foreign matterinspection apparatus applied to performing the foreign matter inspectionmethod will herein be described. Accordingly all of the aforementionedforeign matter inspection methods are applicable to the followingforeign matter inspection apparatus.

An inspection object of the electron beam inspection apparatus is asample 20. The sample 20 is any of a silicon wafer, a glass mask, asemiconductor substrate, a semiconductor pattern substrate, and asubstrate having a metal film. The electron beam inspection apparatusaccording to this embodiment detects presence of a foreign matter 10 onthe surface of the sample 20 that is any one of these substrates. Theforeign matter 10 is insulative material, conductive material,semiconductor material, or a composite thereof. The types of the foreignmatter 10 include particles, cleaning residues (organic matters),reaction products on the surface and the like. The electron beaminspection apparatus may be an SEM type apparatus or a mappingprojection apparatus. In this example, the present technology is appliedto the mapping projection inspection apparatus.

The mapping projection type electron beam inspection apparatus includes:a primary optical system 40 that generates an electron beam; a sample20; a stage 30 on which the sample is mounted; a secondary opticalsystem 60 that forms an enlarged image of secondarily released electronsor mirror electrons from the sample; a detector 70 that detects theelectrons; an image processor 90 (image processing system) thatprocesses a signal from the detector 70; an optical microscope 110 foralignment; and an SEM 120 for review. The detector 70 may be included inthe secondary optical system 60. The image processor 90 may be includedin the image processor.

The primary optical system 40 generates an electron beam, and irradiatesthe sample 20. The primary optical system 40 includes an electron gun41; lenses 42 and 45; apertures 43 and 44; an E×B filter 46; lenses 47,49 and 50; and an aperture 48. The electron gun 41 generates an electronbeam. The lenses 42 and 45 and apertures 43 and 44 shape the electronbeam and control the direction of the electron beam. In the E×B filter46, the electron beam is subjected to a Lorentz force due to a magneticfield an electric field. The electron beam enters the E×B filter 46 inan inclined direction, is deflected into a vertically downwarddirection, and travels toward the sample 20. The lenses 47, 49 and 50control the direction of the electron beam and appropriately decelerate,thereby controlling the landing energy LE.

The primary optical system 40 irradiates the sample 20 with the electronbeam. As described above, the primary optical system 40 performsirradiation with both an electron beam for precharging and an imagingelectron beam. In experiment results, the difference between aprecharging landing energy LE1 and a landing energy LE2 for an imagingelectron beam is preferably 5 to 20 [eV].

In terms of this point, it is provided that in the case with a potentialdifference between the potential of the foreign matter 10 and thepotential therearound, the precharging landing energy LE1 is emitted ina negative charging region. In conformity with the value of LE1, thecharging up voltage varies. This variation is because of variation in arelative ratio of the LE1 and the LE2 (LE2 is a landing energy of theimaging electron beam as described above). If the LE1 is high, thecharging up voltage is high. Accordingly, a reflection point is formedat an upper position of the foreign matter 10 (position close to thedetector 70). The trajectory and transmittance of the mirror electronsvary according to the reflection point. Thus, the optimal charging-upvoltage conditions are determined according to the reflection point. Ifthe LE1 is too low, an efficiency of forming the mirror electronsreduces. The present technology has found that the difference betweenthe LE1 and the LE2 is preferably 5 to 20 [eV]. The value of the LE1 ispreferably 0 to 40 [eV], and further preferably 5 to 20 [eV].

In the primary optical system 40 of the mapping projection opticalsystem, the E×B filter 46 is particularly important. The primaryelectron beam angle can be defined by adjusting the conditions of theelectric field and the magnetic field of the E×B filter 46. Forinstance, the irradiation electron beam of the primary system and theelectron beam of the secondary system can set the conditions of E×Bfilter 46 so as to make the incidence substantially rectangular to thesample 20. In order to further increase the sensitivity, for instance,it is effective to incline the incident angle of the electron beam ofthe primary system with respect to the sample 20. An appropriateinclined angle is 0.05 to 10 degrees, preferably is about 0.1 to 3degrees.

Thus, the signal from the foreign matter 10 is strengthened by emittingthe electron beam at an inclination of a prescribed angle θ with respectto the foreign matter 10. Accordingly, conditions where the trajectoryof the mirror electron does not deviate from the center of the secondaryoptical axis can be formed. Thus, the transmittance of the mirrorelectron can be increased. Accordingly, in the case where the foreignmatter 10 is charged up and the mirror electrons are guided, theinclined electron beam is significantly efficiently used.

Referring again to FIG. 25, the stage 30 is means for mounting thesample 20, and movable in the horizontal x-y directions and the θdirection. The stage 30 may be also movable in the z direction asnecessary. Means for fixing a sample, such as an electrostatic chuck,may be provided on the surface of the stage 30.

The sample 20 is on the stage 30. The foreign matter 10 is on the sample20. The primary optical system 40 irradiates the surface 21 of thesample with the electron beam at a landing energy LE of 5 to −10 [eV].The foreign matter 10 is charged up, incident electrons in the primaryoptical system 40 recoil without coming into contact with the foreignmatter 10. Accordingly, the mirror electrons are guided by the secondaryoptical system 60 to the detector 70. Here, the secondarily releasedelectrons are released from the surface 21 of the sample in spreaddirections. Accordingly, the transmittance of the secondarily releasedelectrons is a low value, for instance, about 0.5 to 4.0%. In contrast,the direction of the mirror electron is not scattered. Accordingly, atransmittance of the mirror electrons of about 100% can be achieved. Themirror electrons are formed on the foreign matter 10. Thus, only thesignal of the foreign matter 10 can achieve a high luminance (the statewith the large amount of electrons). The difference of the luminancefrom the ambient secondarily released electrons and the ratio of theluminance increase, thereby allowing high contrast to be achieved.

As described above, the image of the mirror electron is enlarged at amagnification higher than the optical magnification. The magnificationratio reaches 5 to 50. In typical conditions, the magnification ratio isoften 20 to 30. Here, even if the pixel size is three times as large asthe size of the foreign matter, the foreign matter can be found.Accordingly, high speed and high throughput can be achieved.

For instance, in the case where the size of the foreign matter 10 has adiameter of 20 [nm], it is sufficient that the pixel size is 60 [nm],100 [nm], 500 [nm] or the like. As with this example, the foreign mattercan be imaged and inspected using the pixel size three times as large asthe size of the foreign matter. This feature is significantly excellentfor high throughput in comparison with the SEM system and the like.

The secondary optical system 60 is means for guiding electrons reflectedby the sample 20 to the detector 70. The secondary optical system 60includes lenses 61 and 63, a NA aperture 62, an aligner 64, and adetector 70. The electrons are reflected by the sample 20, and passagain through the objective lens 50, the lens 49, the aperture 48, thelens 47 and the E×B filter 46. The electrons are then guided to thesecondary optical system 60. In the secondary optical system 60,electrons pass through the lens 61, the NA aperture 62 and the lens 63and are accumulated. The electrons are adjusted by the aligner 64, anddetected by the detector 70.

The NA aperture 62 has a function of defining the secondarytransmittance and aberrations. The size and the position of the NAaperture 62 are selected such that the difference between the signalfrom the foreign matter 10 (mirror electron etc.) and the signal fromthe ambient portions (normal portions) is large. Instead, the size andthe position of the NA aperture 62 are selected such that the ratio ofthe signal from the foreign matter 10 with respect to the ambient signalis large. Thus, the S/N ratio can be high.

For instance, it is provided that the NA aperture 62 can be selected ina range of φ50 to φ3000 [μm]. Detected electrons are mixture of mirrorelectrons and secondarily released electrons. In such situations, theaperture size is effectively selected in order to improve the S/N ratioof the mirror electron image. In this case, it is preferred to selectthe size of the NA aperture 62 such that the transmittance of the mirrorelectrons is maintained by reducing the transmittance of the secondarilyreleased electrons.

For instance, in the case where the incident angle of the primaryelectron beam is 3°, the reflection angle of the mirror electrons isabout 3°. In this case, it is preferred to select the size of the NAaperture 62 that allows the trajectory of the mirror electrons to pass.For instance, the appropriate size is φ250 [μm]. Because of thelimitation to the NA aperture (diameter φ250 [μm]), the transmittance ofthe secondarily released electrons is reduced. Accordingly, the S/Nratio of the mirror electron image can be improved. For instance, in thecase where the aperture diameter is from φ2000 to φ250 [μm], thebackground gradation (noise level) can be reduced to ½ or less.

Referring again to FIG. 25, the detector 70 is means for detectingelectrons guided by the secondary optical system 60. The detector 70 hasa plurality of pixels on the surface. Various two-dimensional sensorsmay be adopted as the detector 70. For instance, the detector 70 may beany of a CCD (charge coupled device) and a TDI (time delayintegration)-CCD. These are sensors that convert electrons into lightand then detect signals. Accordingly, photoelectronic conversion meansis required. Thus, electrons are converted into light usingphotoelectronic conversion or a scintillator. Optical image informationis transmitted to the TDI that detects light. The electrons are thusdetected.

Here, an example where the EB-TDI is applied to the detector 70 will bedescribed. The EB-TDI does not require a photoelectronic conversionmechanism and an optical transmission mechanism. The electrons aredirectly incident on the EB-TDI sensor surface. Accordingly, the highMTF (modulation transfer function) and contrast can be acquired withoutdegradation in resolution. Conventionally, detection of small foreignmatters 10 has been unstable. In contrast, use of the EB-TDI can improvethe S/N ratio of a weak signal of the small foreign matters 10.Accordingly, a higher sensitivity can be achieved. The S/N ratioimproves by a factor of 1.2 to 2.

FIG. 12 shows an electron beam inspection apparatus. Here, an example ofthe entire system configuration will be described.

In FIG. 12, the foreign matter inspection apparatus includes: a samplecarrier 190; a mini-environment 180; a load lock 162; a transfer chamber161; a main chamber 160; an electron beam column system 100; and animage processor 90. A conveyance robot in the atmosphere, a samplealignment device, clean air supply mechanism and the like are providedin the mini-environment 180. A conveyance robot in a vacuum is providedin the transfer chamber 161. The robots are arranged in the transferchamber 161 that is always in a vacuum state. Accordingly, occurrence ofparticles and the like due to pressure variation can be suppressed tothe minimum.

The stage 30 that moves in the X and Y directions and the θ (turning)direction is provided in the main chamber 160. An electrostatic chuck isprovided on the stage 30. The sample 20 itself is provided at theelectrostatic chuck. Instead, the sample 20 is held by the electrostaticchuck in a state of being arranged on a pallet or a jig.

The main chamber 160 is controlled by the vacuum control system 150 suchthat the inside of the chamber is kept in a vacuum. The main chamber160, the transfer chamber 161 and the load lock 162 are mounted on avibration isolation base 170. The configuration prevents vibrations fromthe floor from being transmitted.

An electron column 100 is provided on the main chamber 160. The electroncolumn 100 includes: columns of a primary optical system 40 and asecondary optical system 60; and a detector 70 that detects secondarilyreleased electrons, mirror electrons and the like from the sample 20.The signal from the detector 70 is transmitted to the image processor 90and processed. Both on-time signal processing and off-time signalprocessing can be performed. The on-time signal processing is performedduring inspection. In the case of off-time signal processing, only animage is acquired and the signal processing is performed thereafter.Data processed in the image processor 90 is stored in recording media,such as a hard disk and memory. The data can be displayed on a monitorof a console, as required. The displayed data is, for instance, aninspection region, a map of the number of foreign matters, the sizedistribution and map of foreign matters, foreign matter classification,a patch image and the like. System software 140 is provided in order toperform signal processing. An electronic optical system control powersupply 130 is provided in order to supply power to the electron columnsystem. The optical microscope 110 and the SEM inspection apparatus 120may be provided in the main chamber 160.

FIG. 13 shows an example of a configuration in the case where anelectron column 100 and an SEM inspection apparatus 120 of a mappingoptical system inspection apparatus are provided in the same mainchamber 160. The arrangement of the mapping optical system inspectionapparatus and the SEM inspection apparatus 120 in the same chamber 160as shown in FIG. 13 is significantly advantageous. A sample 20 ismounted on the same stage 30. The sample 20 can be observed or inspectedaccording to the mapping system and SEM system. A method of using thisconfiguration and advantageous effects thereof are as follows.

Since the sample 20 is mounted on the same stage 30, the coordinaterelationship is uniquely defined when the sample 20 is moved between themapping system electron column 100 and the SEM inspection apparatus 120.Accordingly, when the detection positions of foreign matters areidentified, two inspection apparatuses can easily highly accuratelyidentify the same position.

In the case where above configuration is not applied, for instance, themapping optical inspection apparatus and the SEM inspection apparatus120 are configured to be separated from each other as differentapparatuses. The sample 20 is moved between the separated apparatuses.In this case, the sample 20 is required to be mounted on the separatestages 30. Accordingly, the two apparatuses are required to separatelyalign the sample 20. In the case of separately aligning the sample 20,specific errors at the same position are unfortunately 5 to 10 [μm]. Inparticular, in the case of the sample 20 with no pattern, the positionalreference cannot be identified. Accordingly, the error furtherincreases.

In contrast, in this embodiment, as shown in FIG. 13, the sample 20 ismounted on the stage 30 in the same chamber 160 in two types ofinspections. Even in the case where the stage 30 is moved between themapping type electron column 100 and the SEM inspection apparatus 120,the same position can be highly accurately identified. Accordingly, evenin the case of the sample 20 with no pattern, the position can be highlyaccurately identified. For instance, the position can be identified atan accuracy of 1 [μm] or less.

Such highly accurate identification is significantly advantageous in thefollowing case. First, foreign matter inspection on the sample 20 withno pattern is performed according to the mapping method. The detectedforeign matter 10 is then identified and observed (reviewed) in detailby the SEM inspection apparatus 120. Since the accurate position can beidentified, not only presence or absence of the foreign matter 10(pseudo-detection in the case of absence) can be determined but also thesize and shape of the foreign matter 10 can be observed in detail athigh speed.

As described above, the separate arrangement of the electron column 100for detecting foreign matters and the SEM inspection apparatus 120 forreviewing takes much time for identifying the foreign matter 10. In thecase of the sample with no pattern, the difficulty is increased. Suchproblems are solved by this embodiment.

As described above, in this embodiment, through use of the apertureimaging conditions for the foreign matter 10 according to the mappingoptical system, a significantly fine foreign matter 10 can be highlysensitively detected. Furthermore, the mapping optical type electroncolumn 100 and the SEM inspection apparatus 120 are mounted in the samechamber 160. Thus, in particular, inspection on the significantly fineforeign matter 10 with a dimension of 30 [nm] or less determination andclassification of the foreign matter 10 can be performed significantlyefficiently at high speed. This embodiment is also applicable to theaforementioned Embodiments 1 to 3 and embodiments to which no numeral isassigned.

Next, another example using both the mapping projection type inspectionapparatus and the SEM will be described.

The above description has been made where the mapping projection typeinspection apparatus detects the foreign matters and the SEM performsreviewing inspection. The two inspection apparatuses can be applied toanother method. Combination of the inspection apparatuses can performeffective inspection. For instance, the other method is as follows.

In this inspection method, the mapping projection type inspectionapparatus and the SEM inspect respective regions different from eachother. Furthermore, the “cell to cell (cell to cell)” inspection isapplied to the mapping projection type inspection apparatus, and the“die to die (die to die)” inspection is applied to the SEM. Accordingly,highly accurate inspection is effectively achieved as a whole.

More specifically, the mapping projection type inspection apparatusperforms “cell to cell” inspection in a region with many repetitivepatterns in the die. The SEM performs the “die to die” inspection in aregion with a small number of repetitive patterns. Both inspectionresults are combined and one inspection result is acquired. The “die todie” inspection compares images of two dice that are sequentiallyacquired. The “cell to cell” inspection compares images of two cellsthat are sequentially acquired. The cell is a part of a die.

The inspection method performs high speed inspection using mappingprojection on repetitive pattern portions while performing inspection onregions with a small number of repetitive patterns using the SEM thatcan achieve high accuracy and small number of artifacts. The SEM is notsuitable to high speed inspection. However, since the region with asmall number of repetitive patterns is relatively narrow, the inspectiontime by the SEM is not too long. Accordingly, the entire inspection timecan be suppressed short. Thus, this inspection method can take advantageof the two methods at the maximum, and perform highly accurateinspection in a short inspection time.

Next, referring again to FIG. 27, the mechanism of conveying the sample20 will be described.

The sample 20, such as a wafer or a mask, is conveyed through a loadport into the mini-environment 180, and an alignment operation isperformed in the environment. The sample 20 is conveyed to the load lock162 by the conveyance robot in the atmosphere. The load lock 162 isevacuated from the atmosphere to a vacuum state by the vacuum pump.After the pressure becomes below a prescribed value (about 1 [Pa]), thesample 20 is conveyed by the conveyance robot in the vacuum disposed inthe transfer chamber 161 from the load lock 162 to the main chamber 160.The sample 20 is mounted on the electrostatic chuck mechanism on thestage 30.

FIG. 14 shows the inside of a main chamber 160 and an electron columnsystem 100 arranged on the top of the main chamber 160. Referencesymbols similar to those of FIG. 11 are assigned to configurationalcomponents similar to those of FIG. 11. The description thereof isomitted.

A sample 20 is mounted on a stage 30 movable in X, Y, Z and θdirections. The stage 30 and an optical microscope 110 perform highlyaccurate alignment. A mapping projection optical system performs foreignmatter inspection and pattern defect inspection of the sample 20 usingan electron beam. Here, the potential of the sample surface 21 isimportant. In order to measure the surface potential, a surfacepotential measurement device capable of measurement in a vacuum isattached to the main chamber 160. The surface potential measurementdevice measures the two-dimensional surface potential distribution onthe sample 20. On the basis of the measurement result, focus control isperformed in a secondary optical system 60 a that forms an electronimage. A focus map of the two-dimensional positions of the sample 20 iscreated on the basis of the potential distribution. Inspection isperformed while changing and controlling the focus under inspection.Accordingly, the blurring and aberrations of an image due to variationin circular potential on the surface according to the position can bereduced. Highly accurate and stable image acquisition and inspection canbe achieved.

Here, the secondary optical system 60 a is configured so as to becapable of measuring detected current of electrons incident on an NAaperture 62 and a detector 70. Furthermore, this system is configuredsuch that an EB-CCD can be arranged on the position of the NA aperture62. Such a configuration is significantly advantageous and effective. InFIG. 14, the NA aperture 62 and the EB-CCD 65 are arranged on a holdingmember 66 that integrally includes openings 67 and 68. The secondaryoptical system 60 a is provided with a mechanism capable ofindependently performing current absorption of the NA aperture 62 andimage acquisition of the EB-CCD 65. In order to achieve this mechanism,the NA aperture 62 and the EB-CCD 65 are arranged in the XY stage 66movable in a vacuum. Accordingly, positional control and positioning canbe performed on the NA aperture 62 and the EB-CCD 65. Since the stage 66is provided with the openings 67 and 68, mirror electrons andsecondarily emitted electrons can pass through the NA aperture 62 or theEB-CCD 65.

The operation of the secondary optical system 60 a having such aconfiguration is described. First, the EB-CCD 65 detects the spot shapeand the center position of a secondary electron beam. The voltages of astigmator, lenses 61 and 63 and an aligner 64 are adjusted such that thespot shape becomes circular and the minimum. In relation to this point,conventionally, the spot shape and astigmatism cannot be directlyadjusted at the position of the NA aperture 62. This embodiment canachieve such direct adjustment, and can highly accurately correct theastigmatism.

Furthermore, the center position of the beam spot can be easilydetected. The position of the NA aperture 62 can be adjusted such thatthe center of the NA aperture 62 is arranged at the beam spot position.In relation to this point, conventionally, direct adjustment of theposition of the NA aperture 62 cannot be performed. This embodiment candirectly adjust the position of the NA aperture 62. Accordingly, the NAaperture can be highly accurately positioned, the aberration of anelectron image is reduced, and uniformity is improved. Thus,transmittance uniformity is improved, thereby allowing an electron imagehaving high resolution and uniform gradation to be acquired.

For inspection of a foreign matter 10, it is important to efficientlyacquire a mirror signal from the foreign matter 10. Since the positionof the NA aperture 62 defines the transmittance and aberration of thesignal, this aperture is significantly important. Secondarily emittedelectrons are emitted at a wide angle range from the sample surfaceaccording to the cosine law, and uniformly reach in a wide region at theNA position (e.g., φ3 [mm]). Accordingly, the secondarily emittedelectrons are insensitive to the position of the NA aperture 62. On thecontrary, the reflection angle of mirror electrons on the sample surfaceis almost equivalent to the incident angle of the primary electron beam.Accordingly, the mirror electrons represent a small divergence, andreach the NA aperture 62 with a small beam diameter. For instance, thedivergent region of mirror electrons is one twentieth as wide as thedivergent region of the secondary electron or less. Accordingly, themirror electrons are significantly sensitive to the position of the NAaperture 62. The divergent region of the mirror electrons at the NAposition is typically a region ranging from φ10 to 100 [μm].Accordingly, it is significantly advantageous and important to acquirethe position with the maximum mirror electron intensity and arrange thecenter position of the NA aperture 62 at the acquired position.

In order to achieve arrangement of the NA aperture 62 at such anappropriate position, according to a preferred embodiment, the NAaperture 62 is moved in X and Y directions in a vacuum in the electroncolumn 100 at an accuracy about 1 [μm]. The signal intensity is measuredwhile the NA aperture 62 is moved. The position with the maximum signalintensity is acquired, and the center of the NA aperture 62 is disposedat the acquired coordinate position.

The EB-CCD 65 is significantly advantageously used for measuring thesignal intensity. This is because two-dimensional information on thebeam can be acquired, the number of electrons entering the detector 70can be acquired to thereby allow the signal intensity to bequantitatively evaluated.

Alternatively, the aperture arrangement may be defined and the conditionof the lens 63 between the aperture and the detector may be configured,so as to achieve a conjugate relationship between the position of the NAaperture 62 and the detection surface of the detector 70. Thisconfiguration is also significantly advantageous. Thus, an image of abeam at the position of the NA aperture 62 is formed on the detectionsurface of the detector 70. Accordingly, a beam profile at the positionof the NA aperture 62 can be observed using the detector 70.

The NA size (aperture diameter) of the NA aperture 62 is also important.The signal region of mirror electrons is small as described above.Accordingly, an effective NA size ranges from about 10 to 200 [μm].Furthermore, it is preferred that the NA size be larger by +10 to 100[%] than the beam diameter.

In relation to this point, the image of electrons is formed of mirrorelectrons and secondarily emitted electrons. The foregoing setting ofthe aperture size can further increase the ratio of mirror electrons.Accordingly, the contrast of the mirror electrons can be increased. Thatis, the contrast of the foreign matter 10 can be increased.

Now, description will be made in further detail. If the aperture is madesmall, the secondarily emitted electrons decrease in inverse proportionto the area of the aperture. Accordingly, the gradation of a normalportion becomes small. However, the mirror signal does not change, andthe gradation of the foreign matter 10 does not change. Thus, thecontrast of the foreign matter 10 can be increased by as much asreduction in gradation therearound, and a high S/N can be achieved.

The aperture may be configured such that the position of the aperturecan be adjusted not only in the X and Y directions but also in the Zaxis direction. This configuration is also advantageous. The aperture ispreferably arranged at a position where the mirror electrons are mostnarrowed. Accordingly, reduction in the aberration of the mirrorelectrons and secondarily emitted electrons can be significantlyeffectively achieved. A higher S/N can therefore be achieved.

As described above, the mirror electrons are significantly sensitive tothe NA size and the shape thereof. Accordingly, appropriate selection ofthe NA size and the shape thereof is significantly important to achievea high S/N. An example of a configuration for selecting such anappropriate NA size and the shape thereof is hereinafter described.Here, the shape of the aperture (hole) of the NA aperture 62 is alsodescribed.

Here, the NA aperture 62 is a member (component) having a hole(opening). Typically, the member is sometimes referred to as anaperture, and the hole (opening) is sometimes referred to as anaperture. In the following description related to the aperture, themember is referred to as an NA aperture in order to discriminate themember (component) from the hole. The hole of the member is referred toas an aperture. The aperture shape is typically referred to as the shapeof a hole.

<Inspection Apparatus>

An inspection apparatus of this embodiment is described with referenceto the drawings. In this embodiment, the case of application to asemiconductor inspection apparatus and the like is exemplified.

As described above, the inspection apparatus of this embodimentincludes: beam generation means for generating any of charged particlesor electromagnetic waves as a beam; a primary optical system thatirradiates, with the beam, an inspection object held in a workingchamber; a secondary optical system that detects secondary chargedparticles emitted from the inspection object; and an image processingsystem that forms an image on the basis of the detected secondarycharged particles.

In this situation, irradiation energy of the beam is set in an energyregion where the mirror electrons are emitted from the inspection objectas the secondary charged particles due to the beam irradiation. Forexample, a landing voltage is set to be not greater than 50 eV.

The secondary optical system includes a camera for detecting thesecondary charged particles, a numerical aperture whose position isadjustable along an optical axis direction and a lens that forms animage of the secondary charged particles that have passed through thenumerical aperture on an image surface of the camera. And, in the imageprocessing system, the image is formed under an aperture imagingcondition where the position of the numerical aperture is located on anobject surface to acquire an image.

Furthermore, the primary optical system includes incident angle controlmeans that controls an incident angle of the beam with which theinspection object is irradiated. Also, the image processing systemincludes shading correction means that provides a shading correctionthat uses a correcting white image and a correcting black image to animage (NA imaging image) formed under the aperture imaging condition. Insuch a situation, the correcting white image is created by adding apredetermined gradation value to the NA imaging image and the correctingblack image is created by subtracting a predetermined gradation valuefrom the NA imaging image. Note that the gradation value to be added tothe NA imaging image may be equal to or different from the gradationvalue to be subtracted from the NA imaging image.

Here, terms, such as secondary charged particles and mirror electrons,are described. “Secondary charged particles” include a part or mixtureof secondarily released electrons, mirror electrons, and photoelectrons.In the case of irradiation with electromagnetic waves, photoelectronsoccur from the surface of the sample. When the surface of the sample isirradiated with charged particles, such as electron beam, “secondarilyreleased electrons” occur from the surface of the sample, or “mirrorelectrons” are formed. The “secondarily released electrons” are causedby collision of an electron beam with the surface of the sample. Thatis, the “secondarily released electrons” are a part or mixture of thesecondary electrons, the reflected electrons, and the backscatteringelectrons. “Mirror electrons” are the emitted electron beam that doesnot collide with the surface of the sample and is reflected in proximityto the surface.

Next, the principle of the present technology will be described withreference to FIG. 15. As shown in FIG. 15A, in the mapping projectionsystem, conventionally, a sample has been irradiated with a primary beamhaving a certain energy, forming an image on the basis of informationabout secondarily released electrons occurring from a sample surface. Atthat time, a landing voltage is between 100 eV and 400 eV. However, inthis conventional method, it has been difficult to acquire a largedifference in contrast because of use of the secondarily releasedelectrons.

Meanwhile, as shown in FIG. 15B, the landing voltage to be used is setto be not greater than 50 eV and mirror electrons that are reflected toreturn back are used. In such a situation, a height at which the mirrorelectrons are reflected changes depending on the state of irregularitiesin a surface, so that a difference in contrast can be created, thusacquiring a large difference in contrast.

Next, the behavior of the mirror electrons will be described. The mirrorelectrons differ in orbit from the secondarily released electrons and amethod that observes this state uses an NA imaging image (an imageacquired under an NA imaging condition). The NA imaging condition meansa condition (secondary system aperture imaging condition) where asecondary system aperture disposed on top of an intermediate lens islocated on an object surface to acquire an image.

The NA imaging condition will be described with reference to FIG. 16. Inan ordinary state that an image is acquired, the image is acquired byimaging in an electron orbit shown by the solid lines in FIG. 16A, butin the NA imaging condition, the image is acquired by imaging in theelectron orbit shown by the dash lines in FIG. 16B. That is, in the NAimaging condition, the state of electrons that have reached the apertureis observed.

And then, a focus adjustment under the NA imaging condition will bedescribed using FIGS. 17 to 20. FIG. 17 is a view illustrating thesecondarily released electrons and the mirror electrons under the NAimaging condition. FIG. 18 is a view illustrating crossover points ofthe mirror electrons and the secondarily released electrons at theaperture as seen from a lateral direction. In FIG. 18, the orbits of themirror electrons are shown in the dash lines and the orbits of thesecondarily released electrons are shown in the solid lines.

As shown in FIGS. 17 and 18, there is a difference in the best focusposition between the mirror electrons and the secondarily releasedelectrons (difference in focus value: for example, about 0.5 mm). And,when the focus is changed, a region of the secondarily releasedelectrons becomes larger as the focus moves toward a plus direction, buta region of the mirror electrons becomes long in a longitudinaldirection and narrow in a lateral direction at a certain focus point,and beyond this focus point, as the focus is moved toward the plusdirection, the region crushes in the longitudinal direction and extendsin the lateral direction. Also, as the focus is conversely moved towarda minus direction, a peak changes to be split into two parts (see FIG.17).

FIG. 19 illustrates how a foreign matter is seen when an image of it isacquired by changing the focus. As shown in FIG. 19A, if the focus ismoved toward the minus direction, the foreign matter is seen in theblack color. Meanwhile, if the focus is moved toward the plus direction,the foreign matter is seen in the white color. In FIG. 19B, the mirrorelectrons from a sample surface are shown by the dash lines, and themirror electrons from foreign matters (defects) are shown by the solidlines. As shown in FIG. 19B, the focus is changed from the minus side tothe plus side, resulting in an increased amount of the mirror electronsthat pass through the aperture from the foreign matters (defects).

Also, FIG. 20 illustrates how a foreign matter having a different sizeis seen when an image of it is acquired. As shown in FIG. 20A, thelarger the defect is, the more the focus at which black changes to whiteshifts to the plus side. And, as shown in FIG. 20B, there is an increasein number of the mirror electrons from the small foreign matter thatpass through the aperture before the mirror electrons from the largeforeign matter do. Note that in FIG. 20B, the mirror electrons from thesmall foreign matter (defect) are shown by the heavy lines (thick solidlines) and the mirror electrons from the large foreign matter (defect)are shown by the thin lines (thin solid lines).

Next, the incident angle adjustment of the primary beam will bedescribed with reference to FIGS. 21 to 27. If an incident angle of theprimary beam deviates, an orbit of the mirror electrons that passthrough the aperture becomes complex. For example, FIG. 21 illustrateshow a foreign matter (defect) is seen when the incident angle of theprimary beam deviates in a vertical direction. As shown in FIG. 21, ifthe incident angle of the primary beam deviates, a foreign matter(defect) cannot be identified on the basis of information about whiteand black. Accordingly, the smaller a foreign matter (defect) is, themore a condition that the foreign matter can be seen in the black coloris lost. Therefore, it becomes necessary to adjust the incident angle ofthe primary beam. Furthermore, as described later, also in the secondarysystem, it becomes necessary to adjust a crossover point of the mirrorelectrons to the aperture (see FIGS. 28 to 32).

FIG. 22 is a view illustrating a conventional adjustment method of anincident angle of a primary beam. In the conventional method, a primarysystem aligner electrode is adjusted so that an orbit of the primarybeam passes through the center of a primary system aperture and acurrent measured value in a Faraday cup becomes maximum. However, inthis conventional method, the incident angle of the primary beam isunable to be confirmed. It is because, in the current measurement in theFaraday cup, only the current that has reached is measured andinformation about an angular component cannot be acquired (if theprimary beams have identical current densities, there is not adifference in current value). However, because an image isconventionally acquired under a condition where the primary beam haslanded, there has not been a problem with the incident angle of theprimary beam.

The incident angle adjustment is provided by using the NA imagingcondition and adjusting a position of the mirror electrons. FIG. 23shows the relation between the mirror electrons and the incident angleof the primary beam on an NA image. As shown in FIG. 23, from an imageacquired by NA imaging, the incident angle of the primary beam can beacquired.

FIG. 24 is a view illustrating how the NA imaging image is seen if theincident angle is different. As shown in FIG. 24A, in the case of normalincidence, the mirror electrons are located in the central area of thesecondarily released electrons. Also, as shown in FIG. 24B, if theincident angle tilts toward a Y axis direction, the mirror electronsdeviate from the secondarily released electrons toward the Y axisdirection. Furthermore, as shown in FIG. 24C, if the incident angletilts toward an X axis direction, the mirror electrons deviate from thesecondarily released electrons toward the X axis direction.

If the incident angle of the primary beam tilts, for example, as shownin FIG. 25, the incident angle can be adjusted by using the alignerelectrode of the primary beam. Also, as shown in FIG. 26, the incidentangle can be adjusted by using a Wien filter (E×B).

In this embodiment, as shown in FIG. 27, irradiation of the primary beamis carried out via E×B. That is, the primary beam is incident on E×Bobliquely from above in the Y axis direction. In such a situation, theincident angle adjustment in the X axis direction can be provided byadjusting an electrode voltage of the primary system aligner in the Xaxis direction. Also, the incident angle adjustment in the Y axisdirection can be provided by using E×B.

Next, the adjustment of the secondary system will be described withreference to FIGS. 28 to 32. FIG. 28 is a view illustrating aconventional adjustment method of the secondary system. As shown in FIG.28, conventionally, in an adjustment method of an imaging condition byusing an electron beam inspection apparatus according to a mappingprojection system, only the optical axis is confirmed. In particular, avoltage value of an electric field lens is automatically changed at acertain value and at a certain frequency, and from a change in image atthis time, whether there is a deviation from the center of the electrodeor not is recognized and if the deviation occurs, the aligner isadjusted so that the optical axis passes through the center of theelectrode. But the conventional technique is an adjustment method forpassing the secondarily released electrons and the mirror electronsthrough the center of the electrode, and a crossover position is notadjusted at the aperture.

When foreign matters are observed by using the mirror electrons, asshown in FIG. 29, it is necessary to align a crossover of the mirrorelectrons emitted from a sample with the center of the aperture. Then,as shown in FIG. 30, the orbit of the mirror electrons is moved to alignthe crossover. For example, an objective lens condition is adjusted sothat the crossover can be aligned. In particular, a focus condition isadjusted by using a focus electrode of the objective lens so that thecrossover point of the mirror electrons can be aligned with the heightof the aperture. Also, newly introducing an adjusting electrode canallow parameter adjustment for the alignment.

There is, for example, a method to move the secondary system aperture inwhich, as shown in FIG. 31, the aperture is brought into a movable statein a Z direction and moved so that the height of the aperture can bemade equal to a height of the crossover point of the mirror electrons.Furthermore, as shown in FIG. 32, the adjustment can be also provided bychanging the focus electrode of the objective lens. Such an adjustmentcan allow an image of fine foreign matters in a sample surface (forexample, foreign matters of 30 nm in size) to be acquired.

Finally, the shading correction will be described with reference toFIGS. 33 to 35. The shading correction can allow smaller foreign matters(for example, foreign matters of 20 nm in size) to be detected.

FIG. 33 is a view illustrating a conventional shading correction. Asshown in FIG. 33, in a conventional correction method, a brighter image(correcting white image) and a darker image (correcting black image)than a raw image are taken in to provide a correction that usescross-section gradation values of these images. For example, thecorrecting white image is created by using a gain of the camera so thatthe raw image approximates the maximum gradation value. Also, thecorrecting black image is created by taking in an image without aprimary irradiation electron beam being projected.

However, in the conventional method, if foreign matters (defects) aresmall, electronic information about the defects (fine defects) is lessand may be mixed with a noise of the image. For example, as shown inFIG. 34A, if a difference between the gradation values of the noise andthe fine defect is not greater than 1, the noise may be detected eventhough a threshold value is adjusted. Therefore, it has been desired tofurther enhance sensitivity.

In this embodiment, the correcting white and black images are set in arange smaller than an actual range of gradation values. Accordingly, asshown in FIG. 34B, information about defects is emphasized. In such asituation, also the noise is emphasized, but the noise can be removedusing the threshold value if it falls within an adjustment range of thethreshold value. For example, the threshold value is, as shown in FIG.34B, adjusted so that only the defect signal can be detected.

FIG. 35 is a view illustrating the shading correction according to thisembodiment. In this embodiment, the raw image is processed to create thecorrecting white image and the correcting black image. In such asituation, a value is calculated in a manner that the defects areemphasized and the noise does not become too large. And, only thegradation value corresponding to the calculated value is added to thegradation value of the raw image, thus creating the correcting whiteimage. Also, only the gradation value corresponding to the added valueis subtracted from the gradation value of the raw image, thus creatingthe correcting black image. Furthermore, also a gain of EB-TDI can beadjusted to create the correcting white image and the correcting blackimage.

For example, if the raw image is acquired in 0 to 255 gradations, theraw image brightened by 40 gradations is used to acquire the correctingwhite image. Also, the raw image darkened by 40 gradations is used toacquire the correcting black image. By using the correcting white imageand the correcting black image, a width of 80 gradations can be enlargedto that of 255 gradations, providing an inspection. As the result, fineforeign matters (for example, foreign matters of 20 nm in size) in asample surface can be detected.

In the inspection apparatus according to such an embodiment, theinspection of irregularities in a surface of an inspection object can beprovided with high contrast.

In this embodiment, when the inspection object is irradiated with thebeam, the mirror electrons are emitted from the inspection object.Because the height at which the mirror electrons are reflected changesdepending on irregularities in the surface of the inspection object, adifference in contrast is generated. Also, the mirror electrons differin orbit from the secondarily released electrons. In such a situation,the image is formed under the imaging condition (aperture imagingcondition) where the position of the numerical aperture is located onthe object surface to acquire an image. That is, the crossover of themirror electrons is aligned with the center of the numerical aperture.Accordingly, the inspection of irregularities in a surface of aninspection object can be provided with high contrast.

Furthermore, in this embodiment, the focus is adjusted under theaperture imaging condition. For example, when the focus is moved towardthe minus direction, the foreign matters in the surface of theinspection object come to be seen in the black color. Conversely, whenthe focus is moved toward the plus direction, the foreign matters in thesurface of the inspection object come to be seen in the white color.Therefore, the inspection of irregularities in a surface of aninspection object can be provided with high contrast.

Also, in this embodiment, the incident angle of the beam with which theinspection object is irradiated is controlled. For example, the incidentangle of the beam with which the inspection object is irradiated iscontrolled so that the incident angle of the beam is made normal.Therefore, the inspection of irregularities in a surface of aninspection object can be provided with high contrast and small foreignmatters (for example, foreign matters of 30 nm in size) can be detected.

Furthermore, in this embodiment, the shading correction that uses thecorrecting white image and the correcting black image is provided to theimage formed under the aperture imaging condition. In such a situation,the correcting white image is created by adding the predeterminedgradation value (for example, 40 gradations) to the image, and thecorrecting black image is created by subtracting the predeterminedgradation value (for example, 40 gradations) from the image. The widthbetween the gradation values of the correcting white image and thecorrecting black image is narrowed, so that irregularities (defects) inan inspection object can be emphasized. Therefore, smaller foreignmatters (for example, foreign matters of 20 nm in size) can be detected.

As stated above, the inspection apparatus has an advantageous effectthat the inspection of irregularities in a surface of an inspectionobject can be provided with high contrast and is useful as, for example,a semiconductor inspection apparatus.

What is claimed is:
 1. A focus adjustment method used in an inspectionapparatus, the inspection apparatus comprising: beam generation meansthat generates any of charged particles and electromagnetic waves as abeam; a primary optical system that irradiates an inspection object heldin a working chamber with the beam; a secondary optical system thatdetects secondary charged particles occurring from the inspectionobject; and an image processing system that forms an image on the basisof the detected secondary charged particles, wherein irradiation energyof the beam is set in an energy region where mirror electrons areemitted from the inspection object as the secondary charged particlesdue to the beam irradiation, the secondary optical system comprises acamera for detecting the secondary charged particles, a numericalaperture whose position is adjustable along an optical axis directionand a lens that forms an image of the secondary charged particles thathave passed through the numerical aperture on an image surface of thecamera, and in the image processing system, the image is formed under anaperture imaging condition where the position of the numerical apertureis located on an object surface to acquire an image, the focusadjustment method comprising: imaging an image under the apertureimaging condition at a certain focus point, and moving the focus towarda plus direction when a region of the mirror electrons in the imagecrushes in the longitudinal direction and extends in the lateraldirection, or moving the focus toward a minus direction when a peak ofthe region of the mirror electrons in the image is split into two parts.2. A focus adjustment method used in an inspection apparatus, theinspection apparatus comprising: beam generation means that generatesany of charged particles and electromagnetic waves as a beam; a primaryoptical system that irradiates an inspection object held in a workingchamber with the beam; a secondary optical system that detects secondarycharged particles occurring from the inspection object; and an imageprocessing system that forms an image on the basis of the detectedsecondary charged particles, wherein irradiation energy of the beam isset in an energy region where mirror electrons are emitted from theinspection object as the secondary charged particles due to the beamirradiation, the secondary optical system comprises a camera fordetecting the secondary charged particles, a numerical aperture whoseposition is adjustable along an optical axis direction and a lens thatforms an image of the secondary charged particles that have passedthrough the numerical aperture on an image surface of the camera, and inthe image processing system, the image is formed under an apertureimaging condition where the position of the numerical aperture islocated on an object surface to acquire an image, the focus adjustmentmethod comprising: imaging an image of a foreign matter under theaperture imaging condition at a certain focus point, and moving thefocus toward a plus direction when the foreign matter is seen in a blackcolor in the image.
 3. The focus adjustment method according to claim 2,wherein the larger the foreign matter is, the more the focus is moved tothe plus side.
 4. The focus adjustment method according to claim 2,wherein the smaller the foreign matter is, the more the focus is movedto the minus side.
 5. A focus adjustment method used in an inspectionapparatus, the inspection apparatus comprising: beam generation meansthat generates any of charged particles and electromagnetic waves as abeam; a primary optical system that irradiates an inspection object heldin a working chamber with the beam; a secondary optical system thatdetects secondary charged particles occurring from the inspectionobject; and an image processing system that forms an image on the basisof the detected secondary charged particles, wherein irradiation energyof the beam is set in an energy region where mirror electrons areemitted from the inspection object as the secondary charged particlesdue to the beam irradiation, the secondary optical system comprises acamera for detecting the secondary charged particles, a numericalaperture whose position is adjustable along an optical axis directionand a lens that forms an image of the secondary charged particles thathave passed through the numerical aperture on an image surface of thecamera, and in the image processing system, the image is formed under anaperture imaging condition where the position of the numerical apertureis located on an object surface to acquire an image, the focusadjustment method comprising: imaging an image of a foreign matter underthe aperture imaging condition at a certain focus point, and moving thefocus toward a minus direction when the foreign matter is seen in awhite color in the image.